Tetramethyl Ammonium Hydroxide TMAH

Tetramethyl Ammonium Hydroxide (TMAH). TMAH, (CH3)4NOH, etchant has been developed more recently for anisotropic etching of silicon. It is relatively safe to use and presents no special disposal issues. It has a very low oxide etch rate and does not attack aluminum if the soluhon contains a certain amount of silicates. However, hillocks tends to develop in this solution.  

FIGURE 1.21. Etch rate of Si(llO) in TMAH as a function of concentration and temperature. After Tabata 

FIGURE 7.28. Dependence of Si(IOO) crystal plane etching rate on the concentration of dissolved silicon in 22% TMAH at 80°C. After Tabata.  

FIGURE 7.29. Etch rate versus voltage of n- and p-type silicon in 25 wt % TMAH solution. After Acero et 

SiOaCOH) and its polymers. The etching mechanism is suggested to be similar to that in KOH. 

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After exposure, the resist film was developed with a 60s immersion in tetramethyl ammonium hydroxide (TMAH) aqueous solution. 

Electroless copper seed layer on TaN surfaces for Cu metallization in the back-end-of-line semiconductor fabrication was also investigated.38 After etching in diluted HF solution and activation with PdCb, the electroless deposition of copper (to be used as a seed layer) was carried out from CuSCVEDTA solution containing Triton X-100, tetramethyl ammonium hydroxide (TMAH), and formaldehyde as a reducing agent of Cu(II) ions. 

Because of the stability of most of the arsenic compounds of interest for speciation studies, nearly all work commences with homogenized, predominantly lyophylized, materials. Extraction of arsenic species from dry and finely ground samples is often performed with methanol/water/chloroform mixtures or just methanol (Luten et al., 1982 Francesconi et al., 1985 Momplaisir et al., 1991 Ballin et al., 1992 ). Methanol and phosphate buffer (1 1) extraction was applied with especially good results for methylated forms of inorganic arsenic (Arenas, 1991). Rather simple approaches are the solubilization of various types of organic materials by treatment with e.g. tetramethyl ammonium hydroxide (TMAH) at ambient temperature for the subsequent determination of inorganic arsenic and its metabolites (Stoeppler and Apel, 1984, Burow and Stoeppler, 1987) and the solubilization of As(lll) and As(V) by treatment with perchloric acid and Fe2(S04)3 at elevated temperatures with subseqent separation and determination of As(lll) and As(V) (Holak and Specchio, 1991). Some speciation procedures based on NaOH treatment will be described under Speciation procedures. 

The behaviour of As(lll) and As(V) in a graphite furnace during the individual steps of the temperature programme was studied by use of the radiotracer As for urine, human serum and hair solubilized with tetramethyl ammonium hydroxide (TMAH). Significant stabilization effects were observed if various metals, including nickel, were used as matrix modifiers. Thus experimental conditions for the determination of arsenic in urine, human serum and hair were optimized. For the determination of the hair soiution, charring at 1200 °C and atomization at 2400 °C were found to be optimal (Krivan and Arpadjan. 1989). 

The samples were homogenized. A portion of the homogenized sample was freeze-dried, while the rest of it was incinerated in a furnace. A standard solution of iodine was prepared from the dissolution of potassium iodide (Special pure grade, Kanto Chemical Co., Inc.) with freshly purified water (ISmegafl cm) prepared in a NANOpure Infinity Ultrapure water system. Tetramethyl ammonium hydroxide (TMAH) was purchased from the Tama Chemical Co. Other chemicals used were special analytical reagent grade. 

Most samples for analysis by plasma emission spectrometry are dissolved in acids, because metal elements are more soluble in acids. The acidic nature of the solution prevents elements from adsorbing onto the surface of the glassware. Some bases, such as tetramethyl ammonium hydroxide (TMAH), are used to prepare solutions but care needs to be taken to avoid the formation of insoluble metal hydroxides. Organic solvents may be used to dissolve organometallic compounds directly or to extract chelated metals from aqueous solution into the solvent as part of separation and preconcentration steps in sample preparation. 

Another interesting approach to wax analysis, simultaneous pyrolysis-alkylation-gas chromatography, was also reported by Challinor, who used tetramethyl ammonium hydroxide (TMAH) to alkylate acids of different waxes, making them more volatile. He concluded that the different waxes may be readily distinguished by the distribution of fatty acid methyl esters and fatty alcohols. 

A report from a forensic science laboratory in 1989 described a technique to pyrolyze synthetic polymer samples and simultaneously chemically derivatize (methylate) the pyrolysis products prior to analysis by capillary GC and GC/MS, a technique that was referred to as simultaneous pyrolysis methylation-capillary gas chromatography (SPM-GC) and SPM-GC/MS. The methylation is caused to take place in situ by the simple expedient of adding a few microliters of methanol containing tetramethyl ammonium hydroxide (TMAH) to the sample in the sample holder of the pyrolysis device. When applied to sediment samples for characterization of the organic matter, this technique is referred to as TMAH-Py-GC/MS. The methylation procedure quite likely allows measurement of many compounds that otherwise would pass undetected. Table 7.8 shows a list of compounds that were identified in programs of river and lake sediments subjected to analysis by TMAH-Py-GC/MS. ... 

Dissolution Measurements. Dissolution rate measurements of the benzophenone series were made on a Perkin-Elmer Dissolution Rate Monitor (DRM-5900) in puddle development mode with 0.25 N KOH developer. The DRM was computer-controlled using Perkin Elmer DRM analytical software (DREAMS 3.0). Measurements of the sulfonyl/carbonyl esters were made with 0.26 N tetramethyl-ammonium hydroxide (TMAH). Reported dissolution rates DRj/i) are at half film thickness. 

Information about the composition of the sample material can be significantly increased if the paints have been derivatized during pyrolysis. Tetramethyl-ammonium hydroxide (TMAH) is used as a derivat-izing reagent for structure elucidation of alkyd, unsaturated polyester, epoxy, and phenol-formaldehyde resins. The derivatization of paints, whose pyrolysis products elute at very low retention times (such as formulations based on polyvinylacetate... 

Porous silicon template could be carefully removed via selective chemical etching in tetramethyl ammonium hydroxide (TMAH) solution at 40-90 °C. Such dissolution process is crucial and not so easy to control. The etch rate is not the same for different Si templates. It depends on the Si dopant type and level as well as on the pore depth and diameter. The removal of template could be done using KOH solution, but the etching behavior is completely different from the case of TMAH. Ethylene diamine pyrocatechol is also reported as a chemical etch solution at 115 °C to successfully... 

Challinor [611,620] has reported the use of pyrolysis derivatisation techniques, simultaneous pyrolysis methylation (SPM), cq. THM. In Py-THM-GC the sample (about 5 /xg) is typically placed in the hollow of a flattened Curie-point pyrolysis wire with approximately 0.5 /u-L tetramethyl ammonium hydroxide (TMAH) (25 wt.% aqueous solution) or tetramethylsulfonium hydroxide (TMSH). The prepared wire is then immediately located in the py-rolyser without allowing aqueous TMAH to evaporate and pyrolysis is carried out at the predetermined temperature. Special injectors for chemolysis (e.g. PTV injector) allow THM also for furnace PyGC experiments. Moldoveanu [499] has listed other common derivatisations utilised in GC analysis. 

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